Access points and access routers are the basic building blocks of wireless access networks. Access points (AP) provide a radio interface to a network by bridging wired segments to wireless segments. The access router (AR) behind the AP provides gateway functionality for the internet protocol (IP) network. Client hosts establish radio links with an AP to communicate with the AR and access the IP network.
In order to connect to the Internet, a client device first has to discover access points in its neighborhood. It might have to do this when it first starts, or when it loses its current network connection due to deteriorating radio conditions. The client device can perform access point discovery by scanning different radio channels. Since there may or may not be any access point on a given channel, this process is usually executed in an exhaustive manner. Depending on the availability of access points and their responsiveness, this process of identifying a next access point can take up to several hundreds of milliseconds with IEEE 802.11b technology, for example.
Once an access point is discovered, the client now has to establish link-layer connectivity with this access point in order to be able to exchange IP packets with the access router. Unless this is an open system (i.e., free network access), this stage involves authentication and authorization of the client. Authentication process usually requires several over-the-air messages accompanied with others over the wired backbone for the access point communicating with the authentication backend server. Because the latter usually involves messaging across the Internet, it is a very costly operation. A successful authentication process can take up to a few seconds to complete.
Once the client has link-layer connectivity, it can proceed to discovering the access router(s) on this link and configure its IP address and default gateway. Depending on the choice of address configuration (e.g., via PPP, DHCP, IPv6 stateless address auto-configuration), this stage can take between tens of milliseconds and a couple of seconds.
Depending on the needs of the client, there can be more stages of discovery, such as, discovering a DNS server, localized mobility management server, IPv4-lPv6 translators or application layer gateways. Any of these operations would have to wait for successful completion of the earlier stages, and therefore cannot be executed in parallel.
When a client desires to get connected to the Internet via an access network, it has to follow a number of stages before it can successfully do so. Going through this complete connection process usually takes on the order of few seconds, during which the client has no IP connection. While being disruptive to any kind of communication, this type of latency is especially unacceptable for delay-sensitive real-time applications, such as voice over IP (VoIP).
The problem becomes magnified when there are several access networks with varying capabilities in the same geography. This type of heterogeneity would exist with WLAN deployments. Each access point might be owned by a different service provider that may or may not allow a particular client in their network. Even after a client has established link-layer connectivity with one of the access points, it might discover that the access router doesn't provide a certain required functionality (e.g., no IPv6 support), or the network is lacking a desired server/service (e.g., SLP). In this case, even though the client has already spent its valuable time trying to use a particular access network, now it might have to start from the beginning and look for another access point. This process also needs to be repeated each time the client has to perform a handover.
The relation between link-layer addresses and IP addresses is characterized as “one-to-many” in conventional networks. That is, a link-layer address can be used with multiple IP addresses on the same host. But a single IP address can only be mapped to one link-layer address. IPv6 Neighbor Discovery [NDISC] protocol is designed in accordance with this model. A neighbor advertisement can provide only one link-layer address for the given target address.
Wireless Internet access is generally unreliable compared to its wired counterpart. A wireless host can experience varying levels of packet loss and connection loss. During the course of a communication, it may change its point of attachment several times due to mobility.
Accordingly, there is a need for a method of associating an IP address with a plurality of link layer addresses in a wireless communication network.